One of the co-inventors of the present invention had invented a torsional vortex sensor providing a maximum immunity to the noise created by the mechanical vibrations of the sensor body, which invention has been disclosed in U.S. Pat. No. 5,101,668. Extensive experimenting with and testing of the vortex flowmeter disclosed in the above-mentioned U.S. Patent indicates that this version of the vortex flowmeter has a construction optimized only in vibration dynamic characteristics, but not in fluid dynamic characteristics. In most occasions, the lateral planar extensions disposed within the flow passage and laterally extending from the vortex sensing planar member in two opposite directions respectively across the two opposite halves of the flow passage divided from one another by the vortex sensing planar member or by the vortex generator-sensor, induces a fluid dynamic instability in the downstream region of the vortex generating bluff body and creates highly detrimental modulation or beating in the intensity of the vortex shedding, even when the vortex sensing planar member has a perfectly symmetric construction with respect to a plane defined by the vortex sensing planar member and dividing the flow passage hypothetically into the two opposite halves. While such a fluid dynamic instability does not alter the functional relationship between the vortex shedding frequency and the fluid velocity, the beating or modulation in the intensity of the vortex shedding produces strong beatings or modulations in an alternating electrical generated by a single or a pair of piezo electric transducers included in the vortex sensor and makes it very difficult to count the vortex shedding frequency. The present invention addresses a solution to the above-described problem by disclosing a torsional vortex sensor that is optimized not only in the vibrational dynamic characteristics but also in the fluid dynamic characteristics.